crc-itu-t: fix typo in CRC ITU-T polynomial comment

The code comment says that the polynomial is x^16 + x^12 + x^15 + 1, but
the correct polynomial is x^16 + x^12 + x^5 + 1. Quoting from page 2 in
the ITU-T V.41 specification [1]:

2 Encoding and checking process

The service bits and information bits, taken in conjunction,
correspond to the coefficients of a message polynomial having terms
from x^(n-1) (n = total number of bits in a block or sequence) down to
x^16. This polynomial is divided, modulo 2, by the generating
polynomial x^16 + x^12 + x^5 + 1.

The hex (truncated) polynomial 0x1021 and CRC code implementation are
correct, however.

[1] https://www.itu.int/rec/T-REC-V.41-198811-I/en

Signed-off-by: Roger Knecht <[e-mail]>
Acked-by: Randy Dunlap <[e-mail]>
Signed-off-by: Jason A. Donenfeld <[e-mail]>

include/linux/crc-itu-t.h

···
  *
  * Implements the standard CRC ITU-T V.41:
  *   Width 16
- *   Poly  0x1021 (x^16 + x^12 + x^15 + 1)
+ *   Poly  0x1021 (x^16 + x^12 + x^5 + 1)
  *   Init  0
  */
 

lib/crc-itu-t.c

···
 #include <linux/module.h>
 #include <linux/crc-itu-t.h>
 
-/** CRC table for the CRC ITU-T V.41 0x1021 (x^16 + x^12 + x^15 + 1) */
+/* CRC table for the CRC ITU-T V.41 0x1021 (x^16 + x^12 + x^5 + 1) */
 const u16 crc_itu_t_table[256] = {
 	0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
 	0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,