UPSTREAM: arm64: Disable PAN on uaccess_enable()

Commit 4b65a5db3627 ("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>

Bug: 31432001
Change-Id: If61cb6cc756affc7df7fa06213723a8b96eb1e80
(cherry picked from commit 75037120e62b58c536999eb23d70cfcb6d6c0bcc)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>