Fix omrgenerate_ieat_dump.s assembly instruction to load 64 bit

One of the load register instructions was meant to be
loading the 64 bit address over which was not apparent while
compiling with XLC. The problem manifested itself as a
segmentation fault with Open XL, and this addresses that issue
while keeping XLC working the same way.

Signed-off-by: Gaurav Chaudhari <gaurav.chaudhari@ibm.com>

port/zos390/omrgenerate_ieat_dump.s

@@ -44,7 +44,7 @@ _TDUMP   EDCXPRLG BASEREG=8
 .JMP1    ANOP
 _TDUMP   CELQPRLG BASEREG=8
 * IEATDUMP macro will toast R1, so keep it in R3
-         LR    3,1
+         LGR   3,1
          USING IOPARMS,3
          CALL  BPX4ENV,                                                +
                (=A(ENV_TOGGLE_SEC),                                    +