usb: xhci: rework Event Ring Segment Table Size mask

usb: xhci: rework Event Ring Segment Table Size mask

Event Ring Segment Table Size Register contain two fields:
 - Bits 15:0:	Event Ring Segment Table Size
 - Bits 31:16:	RsvdZ (Reserved and Zero)

The current mask 'ERST_SIZE_MASK' refers to the RsvdZ bits (31:16).
Change the mask to refer to bits 15:0, which are the Event Ring Segment
Table Size bits.

Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20250515135621.335595-19-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>