avcodec/ccaption_dec: fix EIA-608 Extended Character Set single quote mappings

Fix two incorrect Unicode mappings in the CCSET_EXTENDED_SPANISH_FRENCH_MISC
character set:

1. OPENING SINGLE QUOTE (0x26) was incorrectly mapped to U+00B4 ACUTE ACCENT.
   Per CTA-608-E Section 6.4.2, it should map to U+2018 LEFT SINGLE QUOTATION
   MARK to mirror the standard apostrophe (U+2019), which is already correctly
   mapped in the basic character set.

2. PLAIN SINGLE QUOTE (0x29) was incorrectly mapped to U+2018 LEFT SINGLE
   QUOTATION MARK. It should map to U+0027 APOSTROPHE, the neutral (vertical)
   glyph.

Fixes: https://code.ffmpeg.org/FFmpeg/FFmpeg/issues/21332
Signed-off-by: Sankalpa Sarkar <sankalpasarkar68@gmail.com>

libavcodec/ccaption_dec.c

@@ -108,10 +108,10 @@ enum cc_charset {
         ENTRY(0x23, "\u00da")                            \
         ENTRY(0x24, "\u00dc")                            \
         ENTRY(0x25, "\u00fc")                            \
-        ENTRY(0x26, "\u00b4")                            \
+        ENTRY(0x26, "\u2018")                            \
         ENTRY(0x27, "\u00a1")                            \
         ENTRY(0x28, "*")                                 \
-        ENTRY(0x29, "\u2018")                            \
+        ENTRY(0x29, "'")                                 \
         ENTRY(0x2a, "-")                                 \
         ENTRY(0x2b, "\u00a9")                            \
         ENTRY(0x2c, "\u2120")                            \