arm64: Disable PAN on uaccess_enable()

Commit 4b65a5db ("arm64: Introduce uaccess_{disable,enable}
functionality based on TTBR0_EL1") added conditional user access
enable/disable. Unfortunately, a typo prevents the PAN bit from being
cleared for user access functions.

Restore the PAN functionality by adding the missing '!'.

Fixes: b65a5db3627 ("arm64: Introduce uaccess_{disable,enable} functionality based on TTBR0_EL1")
Reported-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/uaccess.h

@@ -188,7 +188,7 @@ do {									\
 
 #define __uaccess_enable(alt)						\
 do {									\
-	if (uaccess_ttbr0_enable())					\
+	if (!uaccess_ttbr0_enable())					\
 		asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), alt,		\
 				CONFIG_ARM64_PAN));			\
 } while (0)