x86/traps: Correct exc_general_protection() and math_error() return paths

Commit

  334872a0 ("x86/traps: Attempt to fixup exceptions in vDSO before signaling")

added return statements which bypass calling cond_local_irq_disable().

According to

  ca4c6a98 ("x86/traps: Make interrupt enable/disable symmetric in C code"),

cond_local_irq_disable() is needed because the asm return code no longer
disables interrupts. Follow the existing code as an example to use "goto
exit" instead of "return" statement.

 [ bp: Massage commit message. ]

Fixes: 334872a0

 ("x86/traps: Attempt to fixup exceptions in vDSO before signaling")
Signed-off-by: Thomas Tai <thomas.tai@oracle.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Link: https://lkml.kernel.org/r/1617902914-83245-1-git-send-email-thomas.tai@oracle.com