usb: xhci: fix maximum event ring segments calculation

The migration to FIELD_GET introduced an incorrect bit shift.
Instead of raising 2 to the power of the register value, the code
incorrectly used a static shift of 2 (<< 2). This severely limits the
maximum event ring segments on modern controllers.

Fix this by converting the FIELD_GET result to a proper power of two
using the BIT() macro.

Signed-off-by: Mathias Nyman <mathias.nyman@://intel.com>

Author: Mathias Nyman

drivers/usb/host/xhci-mem.c

@@ -2301,7 +2301,7 @@ xhci_alloc_interrupter(struct xhci_hcd *xhci, unsigned int segs, gfp_t flags)
 	if (!segs)
 		segs = ERST_DEFAULT_SEGS;
 
-	max_segs = FIELD_GET(HCS_ERST_MAX, xhci->hcs_params2) << 2;
+	max_segs = BIT(FIELD_GET(HCS_ERST_MAX, xhci->hcs_params2));
 	segs = min(segs, max_segs);
 
 	ir = kzalloc_node(sizeof(*ir), flags, dev_to_node(dev));