remoteproc: fix OOB read via signed offset in rsc_table_for_each_entry()

table->offset[i] is a u32 from firmware, but was stored into a signed
int.  A crafted offset like 0xFFFFFFF0 becomes -16, placing hdr 16 bytes
before the table buffer.  The subsequent avail check was bypassed
because the negative int was promoted to a large size_t in the
expression "table_sz - offset - sizeof(*hdr)", yielding a large positive
avail and letting the out-of-bounds hdr->type read proceed undetected.

Store the offset as u32 and validate it with unsigned comparisons before
any pointer arithmetic.

Signed-off-by: Mukesh Ojha <mukesh.ojha@oss.qualcomm.com>
Fixes: fd2c15ec1dd3 ("remoteproc: resource table overhaul")
Link: https://lore.kernel.org/r/20260803114331.3277263-6-mukesh.ojha@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>