LinuxKPI: acpi; fix type to acpi_get_handle()

The native AcpiGetHandle() and acpi_get_handle() take a
const char * argument for pathname and not an acpi_string (char *).
For that they spell it out fully as 'const char *', so should we.

Sponsored by:	The FreeBSD Foundation (intially)
MFC after:	3 days
Reviewed by:	dumbbell
Differential Revision:	https://reviews.freebsd.org/D52072

Author: Bjoern A. Zeeb

sys/compat/linuxkpi/common/include/acpi/acpi.h

@@ -131,7 +131,7 @@ acpi_format_exception(ACPI_STATUS Exception)
 }
 
 static inline ACPI_STATUS
-acpi_get_handle(ACPI_HANDLE Parent, ACPI_STRING Pathname,
+acpi_get_handle(ACPI_HANDLE Parent, const char *Pathname,
     ACPI_HANDLE *RetHandle)
 {
 	return (AcpiGetHandle(Parent, Pathname, RetHandle));