tcm_fc: remove custom hex_to_bin in ft_parse_wwn

This patch converts ft_parse_wwn() to use hex_to_bin() instead of custom
conversion code.

(Andy: Re-add missing strict && isupper(c) check)

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/tcm_fc/tfc_conf.c

@@ -31,6 +31,7 @@
 #include <linux/types.h>
 #include <linux/string.h>
 #include <linux/configfs.h>
+#include <linux/kernel.h>
 #include <linux/ctype.h>
 #include <asm/unaligned.h>
 #include <scsi/scsi.h>
@@ -70,10 +71,10 @@ static ssize_t ft_parse_wwn(const char *name, u64 *wwn, int strict)
 {
 	const char *cp;
 	char c;
-	u32 nibble;
 	u32 byte = 0;
 	u32 pos = 0;
 	u32 err;
+	int val;
 
 	*wwn = 0;
 	for (cp = name; cp < &name[FT_NAMELEN - 1]; cp++) {
@@ -94,13 +95,10 @@ static ssize_t ft_parse_wwn(const char *name, u64 *wwn, int strict)
 			return cp - name;
 		}
 		err = 3;
-		if (isdigit(c))
-			nibble = c - '0';
-		else if (isxdigit(c) && (islower(c) || !strict))
-			nibble = tolower(c) - 'a' + 10;
-		else
+		val = hex_to_bin(c);
+		if (val < 0 || (strict && isupper(c)))
 			goto fail;
-		*wwn = (*wwn << 4) | nibble;
+		*wwn = (*wwn << 4) | val;
 	}
 	err = 4;
 fail: