sfdisk: remove unnecessary size check [cppcheck]

Following warning is false positive.  Size of the buffer is defined using
BUFSIZ, and so the strncpy() will never overwrite the last byte that is
initialized to zero in get_user_reply().

[disk-utils/sfdisk.c:137] -> [disk-utils/sfdisk.c:136]: (warning) Either the
condition 'bufsz!=0' is redundant or strncpy() argument nr 3 can have
invalid value.  The value is -1 but the valid values are '0:'.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

disk-utils/sfdisk.c

@@ -134,8 +134,6 @@ static int get_user_reply(const char *prompt, char *buf, size_t bufsz)
 		if (!p)
 			return 1;
 		strncpy(buf, p, bufsz - 1);
-		if (bufsz != 0)
-			buf[bufsz - 1] = '\0';
 		free(p);
 	} else
 #endif