bus: omap_l3_noc: fix masterid detection

As per Documentation (OMAP4+), then masterid is infact encoded as
follows:
"L3_TARG_STDERRLOG_MSTADDR[7:0] STDERRLOG_MSTADDR stores the NTTP
master address. The master address is the concatenation of Prefix &
Initiator ConnID. It is defined on 8 bits. The 6 MSBs are used to
distinguish the different initiators."

So, when we matchup currently with the master ID list, we never get a
proper match other than when MPU is the master (thanks to 0).

Now, on other platforms such as AM437x, this tends to be bits[5:0].

Fix this by using the relevant 6MSBits to identify the master ID for
standard and custom errors.

Reported-by: Darren Etheridge <detheridge@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Tested-by: Darren Etheridge <detheridge@ti.com>
Tested-by: Sekhar Nori <nsekhar@ti.com>