[ACPI] acpi_register_gsi() can return error

Current acpi_register_gsi() function has no way to indicate errors to its
callers even though acpi_register_gsi() can fail to register gsi because of
some reasons (out of memory, lack of interrupt vectors, incorrect BIOS, and so
on).  As a result, caller of acpi_register_gsi() cannot handle the case that
acpi_register_gsi() fails.  I think failure of acpi_register_gsi() should be
handled properly.

This series of patches changes acpi_register_gsi() to return negative value on
error, and also changes callers of acpi_register_gsi() to handle failure of
acpi_register_gsi().

This patch changes the type of return value of acpi_register_gsi() from
"unsigned int" to "int" to indicate an error.  If acpi_register_gsi() fails to
register gsi, it returns negative value.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>