SubGhz: refactoring add descriptions (#1012)

* SubGhz: add descriptions
* SubGhz: fix syntax

Co-authored-by: あく <alleteam@gmail.com>

lib/subghz/blocks/math.h

@@ -10,4 +10,10 @@
 #define bit_write(value, bit, bitvalue) (bitvalue ? bit_set(value, bit) : bit_clear(value, bit))
 #define DURATION_DIFF(x, y) ((x < y) ? (y - x) : (x - y))
 
+/**
+ * Flip the data bitwise.
+ * @param key In data
+ * @param count_bit number of data bits
+ * @return Reverse data
+ */
 uint64_t subghz_protocol_blocks_reverse_key(uint64_t key, uint8_t count_bit);