efivars: name the parameters of efi_get_variable() consistently

The definition calls the output parameters ret_attribute, ret_value and
ret_size, as CODING_STYLE asks, but the declaration says attribute and
the stub for builds without EFI support value and size. clang-tidy lets
a prefix difference between declarations pass, while its
bugprone-argument-comment compares argument comments against the first
declaration it sees, so a comment that is right for one build is wrong
for another. Use the definition's names in the declaration and the stub.

src/basic/efivars.h

@@ -39,7 +39,7 @@
 
 #if ENABLE_EFI
 
-int efi_get_variable(const char *variable, uint32_t *attribute, void **ret_value, size_t *ret_size);
+int efi_get_variable(const char *variable, uint32_t *ret_attribute, void **ret_value, size_t *ret_size);
 int efi_get_variable_string(const char *variable, char **ret);
 int efi_get_variable_path(const char *variable, char **ret);
 int efi_set_variable(const char *variable, const void *value, size_t size) _nonnull_if_nonzero_(2, 3);
@@ -52,7 +52,7 @@ SecureBootMode efi_get_secure_boot_mode(void);
 
 #else
 
-static inline int efi_get_variable(const char *variable, uint32_t *attribute, void **value, size_t *size) {
+static inline int efi_get_variable(const char *variable, uint32_t *ret_attribute, void **ret_value, size_t *ret_size) {
         return -EOPNOTSUPP;
 }