[otbn] Fix name of wide data registers

Wide data registers are called WDRs, not WREG.

Signed-off-by: Philipp Wagner <phw@lowrisc.org>

hw/ip/otbn/data/insns.yml

diff --git a/hw/ip/otbn/data/insns.yml b/hw/ip/otbn/data/insns.yml
index 6b5901d..7bbe832 100644
--- a/hw/ip/otbn/data/insns.yml
+++ b/hw/ip/otbn/data/insns.yml
@@ -27,7 +27,7 @@
   - key: bignum
     title: Big Number Instruction Subset
     doc: |
-      All Big Number (BN) instructions operate on the wide register file WREG.
+      All Big Number (BN) instructions operate on the Wide Data Registers (WDRs).
 
 # Instruction encoding schemes
 #