drivers: platform: Mark functions as static in hp_accel.c

This patch marks the functions lis3lv02d_acpi_init(),
lis3lv02d_acpi_read() and lis3lv02d_acpi_write() as static in
x86/hp_accel.c because they are not used outside this file.

Thus, it also eliminates the following warnings in x86/hp_accel.c:
drivers/platform/x86/hp_accel.c:91:5: warning: no previous prototype for ‘lis3lv02d_acpi_init’ [-Wmissing-prototypes]
drivers/platform/x86/hp_accel.c:109:5: warning: no previous prototype for ‘lis3lv02d_acpi_read’ [-Wmissing-prototypes]
drivers/platform/x86/hp_accel.c:132:5: warning: no previous prototype for ‘lis3lv02d_acpi_write’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>