ALSA: seq: Fix function prototype mismatch in snd_seq_expand_var_event

In the Linux kernel, the following vulnerability has been resolved:

ALSA: seq: Fix function prototype mismatch in snd_seq_expand_var_event

With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),

indirect call targets are validated against the expected function

pointer prototype to make sure the call target is valid to help mitigate

ROP attacks. If they are not identical, there is a failure at run time,

which manifests as either a kernel panic or thread getting killed.

seq_copy_in_user() and seq_copy_in_kernel() did not have prototypes

matching snd_seq_dump_func_t. Adjust this and remove the casts. There

are not resulting binary output differences.

This was found as a result of Clang's new -Wcast-function-type-strict

flag, which is more sensitive than the simpler -Wcast-function-type,

which only checks for type width mismatches.